(Reuters) - Center Andrew Bynum would be out indefinitely due to continued problems with his knees, the Philadelphia 76ers said on Saturday.

Bynum has bone bruises in both knees and a "weakened cartilage state", according to doctors and is yet to play for Philadelphia after being part of a four team, 12-player trade that moved him from the Los Angeles Lakers in August.

"Bottom line is Andrew is out indefinitely," 76ers general manager Tony DiLeo said. "There are no timelines. We just have to wait and see how he reacts."

DiLeo said Bynum's knees have deteriorated since arriving in Philadelphia.

"His knees now and the MRIs are not the same; it's a different type (of) situation," DiLeo said.

"At the time of the trade, we had four doctors look at his MRI. We knew it was a calculated risk. We also knew we were getting the second-best center in the league, a franchise-type player. We took that risk."

Bynum has been told to avoid all activities that involve stress on the knees. He is doing low-impact rehabilitation and the team is hoping that rest will heal the cartilage while they consult experts around the world.

"We hope he will back. We're anticipating he will be back at some point," DiLeo said.

"We have plans for the future if he is not back with us but we want to plan on him being here long-term."

DiLeo said Bynum would have further scans in December.

The 25-year-old appeared in 60 games and averaged 18.7 points with 11.8 rebounds for the Lakers last season. He is in the final year of a $16.5 million contract.